In recent years, as power conversion devices for use in high-voltage applications, such as power systems, multilevel converters are put into practical use. The multilevel converters are power converters in which a plurality of converter cells are connected in series to one another, and in which the series connections are further connected in multiple. Those converters are called a modular multilevel converter (MMC), a cascaded multilevel converter (CMC), or the like.
Moreover, it is known that, in the multilevel converters, the converter cells are formed with the use of semiconductor switching elements, such as insulated-gate bipolar transistors (IGBTs) (see Non Patent Literature 1, for example).